The invention relates to a drive system, in particular for a vehicle, comprising a fuel cell unit for generating electrical energy, a secondary battery for storing electrical energy, an electric machine comprising windings and an inverter for actuating the electric machine. The invention furthermore relates to a method for heating a drive system according to the invention.
It will be the case in the future that electronic systems that combine new energy storage technologies with electric drive technology will increasingly be used, in particular, in vehicles, such as hybrid or electric vehicles. To feed three-phase current into an electric machine, a DC voltage from a battery can be converted to a three-phase AC voltage by means of an inverter.
Fuel cells provide one option for generating electrical energy for an electric drive system of a vehicle. In this case, fuel cell vehicles are often also fitted with secondary batteries for storing the electrical energy in order, for example, to provide a temporary power increase for the drive or to make it possible to recuperate braking energy.
DE 10 2012 222 343 A1 discloses a drive system of the generic type for a vehicle. The drive system comprises a fuel cell unit for generating electrical energy, a secondary battery for storing electrical energy, an electric machine and an inverter for actuating the electric machine.
Fuel cells, particularly in automotive uses, can be located during start-up in an environment in which the temperature is low, in particular significantly below freezing. To prevent damage to the fuel cells, it is known to precede normal operation of the fuel cells with a heating phase. In this heating phase, the efficiency of the fuel cell arrangement is usually impaired in order to increase the waste heat production of the fuel cells.
DE 10 2012 218 584 A1 discloses a fuel cell arrangement and a method for heating the fuel cell arrangement. In this case, a connectable electrical resistor is provided between the contacts of the fuel cell arrangement. If said resistor is connected, heat is generated to heat the fuel cell arrangement.
DE 10 2007 026 003 A1 discloses a fuel cell system and a method for cold-starting the fuel cell system. In the case of a cold start of the fuel cell system, electrical loads are connected here and the introduction of reactants is adjusted at the same time.
A method for starting a solid polymer electrolyte fuel cell below the normal operating temperature is known from DE 600 05 836 T2. In this case, the introduction of a reactant during the start time is shortened.
DE 10 2008 029 155 A1 discloses a fuel cell arrangement having flow channels, which has additional means for heating. These means for heating are, for example, an infrared heating apparatus or a heating element.
Inverters for generating a three-phase AC voltage from a DC voltage are known to those skilled in the art. For example, “2014 IEEE, Print ISBN: 978-3-8007-3603-4” and “SIMULATION AND IMPLEMENTATION OF TWO-LEVEL AND THREE-LEVEL INVERTERS BY MATLAB AND RT-LAB, Ohio State University 2011” disclose 3-level inverters, which have a plurality of electronic switches and diodes and a positive pole, a negative pole and a neutral pole.